Medulloblastoma

Medulloblastoma is a malignant small round cell tumour that is found in the cerebellum.

Morphologically identical supratentorial tumours are called primitive neuroectodermal tumour (PNET).

General

• Mostly paediatric population.
• May be seen as a component of nevoid basal cell carcinoma syndrome (NBCCS).
  • Gene: patched (abbreviated PTCH1).
• Commonly spread via cerebrospinal fluid (CSF).
  • May be detected in CSF cytopathology specimens.

Gross

• Location: cerebellum - key feature.
  • Morphologically identical supratentorial tumours are called primitive neuroectodermal tumour (PNET).
  • Supratentorial and spinal metastases from initial tumor possible.

Microscopic

Features:

• Small round cell tumour.
• Homer-Wright rosettes:
  • Rosette with a meshwork of fibers (neuropil) at the centre.

IHC

• MAP2 usu. +ve
• Synaptophysin +ve (weak to strong)
• NSE +ve/-ve
• NF +ve/-ve
• Chromogranin +ve/-ve
• GFAP +ve/-ve (mostly along blood vessels)
• Vimentin +ve
• Nestin +ve
• INI1 retained (no loss)

DDx:

• Small round cell tumours.
  • AT/RT (INI1 loss)
  • CNS-PNET
  • ETMR (LIN28)-positive
  • Ewing Sarcoma family members
  • Small cell glioblastoma

Images

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  Medulloblastoma. (WC/KGH)

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  Medulloblastoma. (WC/KGH)

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  Homer-Wright rosettes in a medulloblastoma. (WC/jensflorian)

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  Cerebellar infiltrative growth. (WC/jensflorian)

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  Demsomplastic nodular medullloblastoma. (WC/jensflorian)

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  Anaplastic large cell medulloblastoma. (WC/jensflorian)

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  Medulloblastoma cells smear. (AFIP)

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  Medulloblastoma in the cerebellum. (AFIP)

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  Reticulin stain highlighting "pale islands" in a desmoplastic medulloblastoma (WC/jensflorian)

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  MIB-1 immunostaining in desmoplastic medulloblastoma (WC/jensflorian)

Case:

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  Classic Medulloblastoma of the SHH type. (WC/jensflorian)

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  Epitheloid ribboning and nuclear moulding of tumor cells. (WC/jensflorian)

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  Areas of geographic necrosis. (WC/jensflorian)

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  Partial MAP2 immunoreactivity. (WC/jensflorian)

www:

• Medulloblastoma (ouhsc.edu).
• Medulloblastoma - several images (upmc.edu).
• Medulloblastoma with rhabdomyoblastic differentiation - several images (upmc.edu).

Subtypes

• Classic medulloblastoma (~85% of all medulloblastomas).
• Variants of medulloblastoma (~15% of all medulloblastomas together):
  1. Anaplastic variant.
  2. Large cell variant.
  3. Desmoplastic/nodular medulloblastoma (DNMB).
  4. Medulloblastoma with extensive nodularity (MBEN).

Notes:

• Prognosis: DNMB & MBEN > classic > anaplastic variant, large cell variant.

Anaplastic variant

Features:

• Larger cells.
• Severe anaplasia.
• Polygonal cells.

See also

• Neuropathology tumours.
• Small round cell tumours.